The invention relates to a method and a hydraulically actuated disc brake having at least one brake piston which acts on a brake pad and which is arranged in a brake housing, along with a parking brake device.
The invention is concerned, in particular, with a method, which is simplified and more failsafe in relation to the prior art, for restoring the brake piston for the purpose of a brake pad exchange.
A piston of a so-called combination brake, which has a parking brake actuating facility and an associated wear adjusting system, is described and illustrated, for example, in the brake handbook by Breuer/Bill, Freidr. Vieweg & Sohn press, 3rd edition, in section “7.2.1.6—Kombinierter Faustsattel [Combined floating caliper]”. The restoration of the piston for the purpose of a brake pad exchange requires the adjusting nut to be turned back on the thread of the adjusting screw. Although the thread is not self-locking, the rotation of the adjusting nut is hindered by means of friction on the brake piston so that, when the parking brake is applied, the clamping force can be transmitted via the thread and the friction to the brake piston. Special tools are required for turning back the adjusting nut, and as a result of the rotational movement of the brake piston, the seals (piston sealing ring, dust protection flap), which are in contact with the brake piston, can be influenced in terms of their action, or damaged.
DE 196 04 402 describes a device in which the necessity for turning back the piston is avoided. A problem with this solution is, however, the necessity for inserting different screws into the central threaded through hole in the piston head for operating and for servicing the brake. Here, there is the risk of the servicing screw not being removed after the servicing work, thereby making the adjusting device and, ultimately, the parking brake inoperative.
Another solution for preventing the rotation of the piston in order to restore the latter is implemented in “Brembo”-type brakes, for example. In such brakes, the piston head is provided with a large opening through which a special restoring piston can be accessed. To restore the brake piston, the restoring piston is placed in engagement, by way of an axial movement, with the adjusting nut so as to transmit a rotational movement. By rotating the restoring piston, the adjusting nut is now turned back, as a result of which the brake piston can be restored by being simultaneously turned back.
The described methods are implemented in floating-caliper brakes. In brakes of this type, the brake caliper must be dismounted for the purpose of a brake pad exchange, since the brake pads are otherwise inaccessible for a brake pad exchange. When the brake calipers are dismounted, the described working processes for restoring the piston can be carried out with relative ease, since sufficient space is available.
In heavy utility or commercial vehicles, use is preferably made of frame calipers, whose particular advantage is that the relatively heavy brake caliper need not be dismounted and removed from the brake disc for the purpose of a brake pad exchange, since the brake pads can be removed through the frame opening of the brake caliper with ease. When the brake is installed, very unfavorable conditions are present for restoring the brake piston, on account of the brake often being positioned in a poorly accessible location and on account of the small distance between the brake disc and the housing part of the frame caliper. The previously described methods can only be carried out in a very cumbersome and time-consuming manner, which leads to increased servicing costs and also to servicing errors.
Against this background, it is intended to find a servicing method and an associated design of the hydraulic brake with an integrated parking brake, in which the restoration of the brake piston—similarly to the simple hydraulic brake—takes place merely by pushing back the piston.
According to the invention, a hydraulically activated disc brake is provided having at least one brake piston, which acts on a brake pad and which is arranged in a brake housing, along with a parking brake device. A restoring piston is held in a piston head, which piston head faces toward the brake pad of the brake piston.
In one embodiment, during a hydraulic actuation of the brake, the restoring piston bears against a contact shoulder of the adjusting nut under the action of pressure, and thereby maintains frictional contact, counter to the force of the restoring spring, in the friction cone coupling in order to prevent a rotation of the adjusting nut. In this state, in the release direction of the cone coupling, the restoring piston has a small spacing with respect to the adjusting nut with the interposed axial bearing, which spacing ensures a minimum play even taking into consideration tolerances and operational deformations. On the side facing toward the brake pad, the restoring piston has a defined projecting length with respect to the contact surface in the depression of the piston head.
In another variant, during a hydraulic actuation of the brake, the restoring piston bears against a contact shoulder of the brake piston under the action of the pressure. In this state, the restoring piston has a small spacing with respect to the adjusting nut with the interposed axial bearing, which spacing ensures a minimum play even taking into consideration tolerances and operational deformations. On the side facing toward the brake pad, the restoring piston has a defined projecting length with respect to the contact surface in the depression of the piston head.
For restoring the piston, a spacer is inserted into the depression of the piston head, which spacer is supported, on the side facing away from the piston, against the brake disc. In the case of multi-piston brakes, spacers of this type are inserted into all the pistons. The sliding caliper is now pushed in the direction of the brake disc. Here, the spacer bears against the contact surface in the depression of the piston head and pushes the restoring piston back until the latter likewise bears against the contact surface. During this rearward pushing movement, the restoring piston sets down via the axial bearing on the end surface of the adjusting nut and raises the latter with its friction cone up from its seat in the piston. The adjusting nut passes out of its frictionally locked state and may now be turned back, as the brake piston is pushed back further, in the non-self-locking thread of the adjusting screw under the action of the axial force.
The restoring of the brake piston is therefore achieved, after the insertion of the spacer, by simply pushing the brake caliper. Alternatively, with the brake caliper fixed, the restoring of the piston may also be effected by exerting pressure on the spacer.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.